1. Field of the Invention
The present invention relates to a diffraction grating element.
2. Related Background of the Invention
A diffraction grating element generally has a diffraction grating formed on a first surface of a transparent plate that comprises the first surface and a second surface that are parallel with one another (see Kashiko Kodate, “Development of diffractive optics and future challenges”; Japan Women's University Journal, Faculty of Science, 10th Edition, pages 7 to 24 (2002), for example). With this diffraction grating element, when, for example, light enters the first surface from a medium that is in contact with the first surface at a constant angle of incidence, this light is diffracted by the diffraction grating formed on the first surface, transmitted within the transparent plate, and then emitted to the medium in contact with the second surface. The diffraction angle of the light emitted from the second surface of the transparent plate varies according to the wavelength.
Therefore, the diffraction grating element can be used as a optical demultiplexer that demultiplexes incident light and emits the demultiplexed light. Further, when the light is guided in the opposite direction to this case, this diffraction grating element can be used as an optical multiplexer that multiplexes the incident light and emits the multiplexed light. In addition, by combining the diffraction grating element with other optical elements, a dispersion regulator that regulates the group delay time of the light in accordance with the wavelength can also be constituted, for example. Therefore, the diffraction grating element is one important optical device in a wavelength division multiplexing (WDM) optical communication system that multiplexes multiple wavelength signal light and then transmits this multiplexed light.